Last week, Microsoft released 14 security bulletins as part of Patch Tuesday for November 2014. The updates contained four rated as critical, including a vulnerability that affects the Windows Secure Channel (SChannel) security package.

But interestingly, two updates originally scheduled for release last week (MS14-068 and MS14-075), were held back.

On Tuesday, Nov. 18, in an out-of-band update, Microsoft released security bulletin MS14-068. Rated as critical, the patch addresses a vulnerability in Microsoft Windows Kerberos KDC that could allow an attacker to elevate unprivileged domain user account privileges to those of the domain administrator account.

Microsoft said the vulnerability has been exploited in limited, targeted attacks.

“An attacker that successfully exploited this vulnerability could impersonate any user on the domain, including domain administrators, and join any group,” Microsoft explained. “By impersonating the domain administrator, the attacker could install programs; view, change or delete data; or create new accounts on any domain-joined system.”

The flaw, which was privately reported to Microsoft, requires that an attacker have valid domain credentials to be exploited. The affected component is available remotely to users who have standard user accounts with domain credentials; this is not the case for users with local account credentials only, Microsoft explained.

Why did Microsoft hold back on releasing the patch last week? The answer is unclear, but it could be for a number of reasons.

“It is not uncommon for a bad patch to be pulled during the QA process,” Tyler Reguly, manager of security research at TripWire, told SecurityWeek.

Reguly also suggested that Microsoft may have considered rethinking their release date this month due to Veteran's Day in the US and Remembrance Day in commonwealth nations, to ensure IT/IS teams were available and fully staffed to react to the massive patch drop.

“MS14-068 was originally scheduled to be released with November’s patch Tuesday and was held back, presumably due to a potential for a negative side effect of the patch or some question about the completeness of the patch," Ross Barrett, senior manager of security engineering at Rapid7, told SecurityWeek. "Obviously because Microsoft is aware of ‘limited targeted attacks’ they were motivated to get the fix out as soon as possible, rather than wait for December."

Regardless of the reason, users should apply the security update (MS14-068) as soon as possible.

“The mitigating factor here is that an attacker must have already authenticated as a valid domain user to exploit this vulnerability,” Barrett added.

For more than 10 years, Mike Lennon has been closely monitoring the threat landscape and analyzing trends in the National Security and enterprise cybersecurity space. In his role at SecurityWeek, he oversees the editorial direction of the publication and is the Director of several leading security industry conferences around the world.